In the production of power from a system using a Rankine cycle, it is proposed to use a power generation unit capable of being used anywhere a source of low-grade thermal energy is available as a heat source and employing an organic fluid as the working fluid in the unit. Such a power unit is capable of producing output power in a relatively low range, such as 1-5 kilowatts where the output is electrical power, while operating efficiently.
As disclosed in copending U.S. application Ser. No. 804,400, filed Dec. 4, 1985, entitled "Power Unit For Converting Heat To Power", such a power unit using an organic Rankine cycle with refrigerant as the working fluid has a constrained, rotary vane expander as a power output unit, a boiler to produce pressurized vapor for operating the expander, a condenser to condense the exhausted vapor, hot and cold side heat exchange circuits, and simple controls for operating the unit when producing power output from a wide possibility of locally available heat sources.
With this system, oil may be injected into the expander for lubrication where it is mixed with refrigerant. An oil separator is provided to separate the oil from the refrigerant.